
01d2b7c287ed6fc0a8ea9c20ec3f67b9.ppt
- Количество слайдов: 64
Alkenes, Reactions
R-H R-X R-OH R-O-R NR NR some NR NR Metals NR NR Oxidation NR NR NR Reduction NR NR NR Halogens NR NR Acids Bases Alkenes
Alkenes, reactions. Addition ionic free radical Reduction Oxidation Substitution
Reactions, alkenes: 1. Addition of hydrogen (reduction). 2. Addition of halogens. 3. Addition of hydrogen halides. 4. Addition of sulfuric acid. 5. Addition of water (hydration). 6. Addition of aqueous halogens (halohydrin formation). 7. 7. Oxymercuration-demercuration.
8. Hydroboration-oxidation. 9. Addition of free radicals. 10. Addition of carbenes. 11. Epoxidation. 12. Hydroxylation. 13. Allylic halogenation 14. Ozonolysis. 15. Vigorous oxidation.
1. Addition of hydrogen (reduction). 2. | | 3. — C = C — + H 2 + Ni, Pt, or Pd — C — 4. | | 5. H H 6. a) Requires catalyst. b) #1 synthesis of alkanes c) CH 3 CH=CHCH 3 + H 2, Ni CH 3 CH 2 CH 3 d) 2 -butene n-butane
Alkanes Nomenclature Syntheses 1. addition of hydrogen to an alkene 2. reduction of an alkyl halide a) hydrolysis of a Grignard reagent b) with an active metal and acid 3. Corey-House Synthesis Reactions 1. halogenation 2. combustion (oxidation) 3. pyrolysis (cracking)
heat of hydrogenation: CH 3 CH=CH 2 + H 2, Pt CH 3 CH 2 CH 3 + ~ 30 Kcal/mole ethylene 32. 8 propylene 30. 1 cis-2 -butene 28. 6 trans-2 -butene 27. 6 isobutylene 28. 4
fats & oils: triglycerides O CH 2—O—CCH 2 CH 2 CH 2 CH 2 CH 3 | O CH 2—O—CCH 2 CH 2 CH 2 CH 3 “saturated” fat
O CH 2—O—CCH 2 CH 2 CH=CH 2 CH 2 CH 2 CH 3 | O CH 2—O—CCH 2 CH=CHCH 2 CH 3 Ω - 3 “unsaturated” oil
Saturated triglycerides are solids at room temperature and are called “fats”. butter fat, lard, vegetable shortening, beef tallow, etc. Unsaturated triglycerides have lower mp’s than saturated triglycerides. Those that are liquids at room temperature are called “oils”. (All double bonds are cis-. ) corn oil, peanut oil, Canola oil, cottonseed oil, etc.
polyunsaturated oils + H 2, Ni saturated fats liquid at RT solid at RT oleomargarine butter substitute (dyed yellow) Trans-fatty acids formed in the synthesis of margarine have been implicated in the formation of “bad” cholesterol, hardening of the arteries and heart disease.
2. Addition of halogens. | | —C=C— + X 2 | | —C—C— | | X X a) X 2 = Br 2 or Cl 2 b) test for unsaturation with Br 2 c) CH 3 CH 2 CH=CH 2 + Br 2/CCl 4 CH 3 CH 2 CHCH 2 d) Br Br e) 1 -butene 1, 2 dibromobutane
3. Addition of hydrogen halides. | | — C = C — + HX — C — | | H X a) HX = HI, HBr, HCl b) Markovnikov orientation c) d) CH 3 CH=CH 2 + e) f) g) CH 3 CH 2 C=CH 2 + HI HBr CH 3 CHCH 3 I CH 3 CCH 3 Br
Markovnikov’s Rule: In the addition of an acid to an alkene the hydrogen will go to the vinyl carbon that already has the greater number of hydrogens.
CH 3 CH 2 CH=CH 2 + CH 3 CH=CCH 3 + CH 3 CH=CHCH 3 + HCl HBr HI CH 3 CH 2 CHCH 3 Cl CH 3 CH 2 CCH 3 Br CH 3 CH 2 CHCH 3 I
An exception to Markovikov’s Rule: CH 3 CH=CH 2 + CH 3 C=CH 2 + HBr, peroxides “anti-Markovnikov” orientation note: this is only for HBr. CH 3 CH 2 Br CH 3 CHCH 2 Br
Markovnikov doesn’t always correctly predict the product! CH 3 CH 2=CHCHCH 3 + HI CH 3 CH 2 CCH 3 I Rearrangement!
why Markovinkov? CH 3 CH=CH 2 + HBr CH 3 CHCH 2 | H or? + Br- CH 3 CHCH 2 | H CH 3 CHCH 3 | Br 1 o carbocation 2 o carbocation more stable
In ionic electrophilic addition to an alkene, the electrophile always adds to the carbon-carbon double bond so as to form the more stable carbocation.
4. Addition of sulfuric acid. 5. | | —C=C— + H 2 SO 4 | | —C—C— | | H OSO 3 H alkyl hydrogen sulfate Markovnikov orientation. CH 3 CH=CH 2 + H 2 SO 4 CH 3 CHCH 3 O O-S-O OH
5. Addition of water. | | —C=C— + H 2 O, H+ | | —C—C— | | H OH a) requires acid b) Markovnikov orientation c) low yield CH 3 CH 2 CH=CH 2 + H 2 O, H+ CH 3 CH 2 CHCH 3 OH
| | — C = C — + H 2 O H+ | | —C—C— | | OH H Mechanism for addition of water to an alkene to form an alcohol is the exact reverse of the mechanism (E 1) for the dehydration of an alcohol to form an alkene.
How do we know that the mechanism isn’t this way? One step, concerted, no carbocation
CH 3 CH=CH 2 + Br 2 + H 2 O + Na. Cl CH 3 CHCH 2 + Br Br CH 3 CHCH 2 OH Br + CH 3 CHCH 2 Cl Br
Some evidence suggests that the intermediate is not a normal carbocation but a “halonium” ion: | | —C—C— Br The addition of X 2 to an alkene is an anti-addition.
6. Addition of halogens + water (halohydrin formation): 7. | | 8. — C = C — + X 2, H 2 O — C — + HX 9. | | 10. OH X a) X 2 = Br 2, Cl 2 b) Br 2 = electrophile c) CH 3 CH=CH 2 + Br 2(aq. ) CH 3 CHCH 2 + HBr d) OH Br
1. 7. Oxymercuration-demercuration. | | — C = C — + H 2 O, Hg(OAc)2 — C — + acetic | | acid OH Hg. OAc | | — C — + Na. BH 4 | | OH Hg. OAc | | —C—C— | | OH H alcohol
oxymercuration-demercuration: a) #1 synthesis of alcohols. b) Markovnikov orientation. c) 100% yields. d) no rearrangements e) CH 3 CH 2 CH=CH 2 + H 2 O, Hg(OAc)2; then Na. BH 4 f) g) CH 3 CH 2 CHCH 3 OH
With alcohol instead of water: alkoxymercuration-demercuration: | | — C =C — + ROH, Hg(TFA)2 — C — | | OR Hg. TFA | | — C — + Na. BH 4 | | OR Hg. TFA | | —C—C— | | OR H ether
alkoxymercuration-demercuration: a) #2 synthesis of ethers. b) Markovnikov orientation. c) 100% yields. d) no rearrangements e) CH 3 CH=CH 2 + CH 3 CHCH 3, Hg(TFA)2; then Na. BH 4 f) OH g) CH 3 h) CH 3 CH-OCHCH 3 i) j) diisopropyl ether k) l) Avoids the elimination with 2 o/3 o RX in Williamson Synthesis.
Ethers nomenclature syntheses 1. Williamson Synthesis 2. alkoxymercuration-demercuration reactions 1. acid cleavage
1. 8. Hydroboration-oxidation. | | — C = C — + (BH 3)2 — C — | | diborane H B— | | | — C — + H 2 O 2, Na. OH | | H B— | | | —C—C— | | H OH alcohol
hydroboration-oxidation: a) #2 synthesis of alcohols. b) Anti-Markovnikov orientation. c) 100% yields. d) no rearrangements e) CH 3 CH 2 CH=CH 2 + (BH 3)2; then H 2 O 2, Na. OH f) g) CH 3 CH 2 CH 2 -OH
CH 3 C=CH 2 + H 2 O, Hg(OAc)2; then Na. BH 4 Markovnikov CH 3 CCH 3 OH CH 3 C=CH 2 + (BH 3)2; then H 2 O 2, Na. OH anti-Markovnikov CH 3 CHCH 2 OH
Alcohols: nomenclature syntheses 1. oxymercuration-demercuration 2. hydroboration-oxidation 3. 4. hydrolysis of a 1 o / CH 3 alcohol 5. 6. 8.
1. 9. Addition of free radicals. | | — C = C — + HBr, peroxides — C — | | H X a) anti-Markovnikov orientation. b) free radical addition c) HI, HCl + Peroxides CH 3 CH=CH 2 + HBr, peroxides CH 3 CH 2 -Br
Mechanism for free radical addition of HBr: Initiating steps: 1) peroxide 2 radical • 2) radical • + HBr radical: H + Br • (Br • electrophile) Propagating steps: 3) Br • + CH 3 CH=CH 2 CH 3 CHCH 2 -Br (2 o free radical) • 4) CH 3 CHCH 2 -Br + HBr CH 3 CH 2 -Br + Br • • 3), 4), 3), 4)… Terminating steps: 5) Br • + Br • Br 2 6) Etc.
In a free radical addition to an alkene, the electrophilic free radical adds to the vinyl carbon with the greater number of hydrogens to form the more stable free radical. In the case of HBr/peroxides, the electrophile is the bromine free radical (Br • ). CH 3 CH=CH 2 + HBr, peroxides CH 3 CH 2 -Br
1. 10. Addition of carbenes. 2. | | 3. — C = C — + CH 2 CO or CH 2 N 2 , hν C— 4. 5. • CH 2 • the 6. 7. | | 8. — C = C — 9. 10. • CH 2 • | | —C— CH 2 “carbene” adds across double bond
| | —C=C— + CHCl 3, t-Bu. OK -HCl | | — C— C — CCl 2 • CCl 2 • dichlorocarbene | | —C=C— • CCl 2 •
11. Epoxidation. | | —C=C— C 6 H 5 CO 3 H + (peroxybenzoic acid) | | — C— C — O epoxide Free radical addition of oxygen diradical. | | —C=C— • O •
12. Hydroxylation. (mild oxidation) | | — C = C — + KMn. O 4 — C — | | OH OH syn OH | | — C = C — + HCO 3 H — C — anti peroxyformic acid | | OH glycol
CH 3 CH=CHCH 3 + KMn. O 4 CH 3 CH-CHCH 3 OH OH 2, 3 -butanediol test for unsaturation purple KMn. O 4 brown Mn. O 2 CH 2=CH 2 + KMn. O 4 CH 2 OH OH ethylene glycol “anti-freeze”
1. 13. Allylic halogenation. 2. | | | 3. — C = C — + X 2, heat — C = C — + HX 4. | | 5. H allyl X 6. CH 2=CHCH 3 + Br 2, 350 o. C CH 2=CHCH 2 Br + HBr 7. a) X 2 = Cl 2 or Br 2 8. b) or N-bromosuccinimide (NBS)
CH 2=CHCH 3 + Br 2 CH 2 CHCH 3 Br Br addition CH 2=CHCH 3 + Br 2, heat CH 2=CHCH 2 -Br + HBr allylic substitution
1. 14. Ozonolysis. 2. | | 3. — C = C — + O 3; then Zn, H 2 O — C = O + O = C— 4. used for identification of alkenes 5. CH 3 6. CH 3 CH 2 CH=CCH 3 + O 3; then Zn, H 2 O 7. 8. O=CCH 3 CH 2 CH=O + CH 3
1. 15. Vigorous oxidation. 2. =CH 2 + KMn. O 4, heat CO 2 3. =CHR + KMn. O 4, heat RCOOH carboxylic acid 4. =CR 2 + KMn. O 4, heat O=CR 2 ketone
CH 3 CH 2 CH=CH 2 + KMn. O 4, heat CH 3 CH 2 COOH + CO 2 CH 3 C=CHCH 3 + KMn. O 4, heat CH 3 C=O + HOOCCH 3
KMn. O 4 CH 3 CHCHCH 3 OHOH mild oxidation glycol CH 3 CH=CHCH 3 + vigorous oxidation hot KMn. O 4 2 CH 3 COOH
Reactions, alkenes: 1. Addition of hydrogen 2. Addition of halogens 3. Addition of hydrogen halides 4. Addition of sulfuric acid 5. Addition of water/acid 6. Addition of halogens & water (halohydrin formation) 7. 7. Oxymercuration-demercuration
8. Hydroboration-oxidation 9. Addition of free radicals 10. Addition of carbenes 11. Epoxidation 12. Hydroxylation 13. Allylic halogenation 14. Ozonolysis 15. Vigorous oxidation
CH 3 C=CH 2 isobutylene “ “ “ + H 2, Pt CH 3 CHCH 3 + Br 2/CCl 4 CH 3 C-CH 2 Br Br + H 2 SO 4 CH 3 CCH 3 Br CH 3 CCH 3 O SO 3 H
CH 3 C=CH 2 isobutylene “ + H 2 O, H+ + Br 2(aq. ) CH 3 CCH 3 OH CH 3 C-CH 2 Br OH CH 3 C=CH 2 + H 2 O, Hg(OAc)2; then Na. BH 4 CH 3 CCH 3 OH “ + (BH 3)2; then H 2 O 2, OH- CH 3 CHCH 2 OH
CH 3 C=CH 2 isobutylene “ “ + HBr, peroxides CH 3 CHCH 2 Br + CH 2 CO, hv CH 3 C–CH 2 CH 3 C–CH 2 O + PBA
CH 3 C=CH 2 isobutylene “ “ “ + KMn. O 4 CH 3 C–CH 2 OH OH CH 3 + Br 2, heat CH 2 C=CH 2 + HBr Br CH 3 + O 3; then Zn/H 2 O CH 3 C=O + O=CH 2 + KMn. O 4, heat CH 3 C=O + CO 2